The invention is intended for integrated decontamination of soils contaminated with mercury (amalgam) and/or radionuclides. The invention provides fractioning of soils for pure coarse- and medium disperse (sand) fractions, as well as fine particle fractions containing water-insoluble forms of mercury or/and radionuclides, and extraction of metal mercury or its amalgam.
Industrial accidents of various nature, decommissioning and dismantling of nuclear fuel cycle facilities and other sectors of industry lead to emerging of territories with soils contaminated with heavy metals, including radionuclides and mercury. Getting into the environment, radionuclides participate in migration processes, having a long-term negative impact on ecosystems. Soils contaminated with metal mercury are no less hazardous: toxic vapour, high probability of their convective transfer and, as a result—subsequent precipitation and contamination of adjacent and remote areas. Therefore, there is a need to develop reliable high-performance methods for soil decontamination with subsequent remediation of contaminated territories.
There is a known patent No. RU2160165 Process line for reprocessing of metal-bearing sands with gravity concentrator, pub. 10.12.2000, for enrichment of refractory gold ores and alluvial deposits with subsequent extraction of metal mercury.
The process line for reprocessing of metal-bearing sands includes disintegrating classifier, initial enrichment device, gravity concentrator, collectors, pumping system, concentrator, device for mercury distillation in the closed cycle, device for gold melting with absorber. The collector of initial enrichment is equipped with amalgamation holders and device for repositioning of holders. The pumping system provides supply of heavy minerals of initial enrichment stage after their amalgamation to the distributor of pulp flows of the gravity concentrator with multi-radius few-row flow-forming surface with riffles, with chequer-wise shift of flows at the output, equipped with magnets installed in front of the flow shifting space at the output, collector of mineral inclusions sorbing mercury, and collector of magnetic fraction equipped with amalgamation holders with automatic device to control holders.
Invention disadvantages—the proposed method and the device do not provide decontamination of soils from heavy metals, such as radionuclides and mercury.
There is a mobile complex for reprocessing and disposal of industrial wastes from precious metal plants, coal cleaning plant (disposed area, sludge depositories) etc., which along with precious metals may contain radionuclides, mercury (amalgam) and other heavy metals (Mining industry, 2009, No. 4, p. 42-49),
which includes the following procedures:                removal of coarse fraction (more than 50 mm);        removal of fraction from 2 to 50 mm and preparation of pulp from the remaining material by mixing it with circulating water;        disintegration of soil aggregates, dispersion of pulp;        hydroclassification of pulp to receive fine particle fractions and sand fractions being a mixture of minerals, precious metals, metal mercury, including amalgam, as well as other heavy metals;        concentration of sand fractions and extraction of precious metals, metal mercury, including amalgam, as well as other heavy metals;        settling, flocculation and thickening of fine particle fraction received at hydroclassification and concentration stages by adding flocculent;        treatment of circulating water from coarse dispersion and soluble forms of heavy metals.        
Thickened fine particle fraction received by reprocessing is sent for recycling. Contaminants extracted at the stage of circulating water treatment are sent for storage and disposal of radioactive waste or toxic substances.
Invention Disadvantages:                extraction of metal mercury (amalgam) after pulp hydroclassification that can lead to its getting into pure fractions;        use of chemical agents for thickening of the fine particle fraction increases volume of rinse waters and consequently material costs;        the method is not appropriate for decontamination of soils because of significant differences between their mineralogic and grain-size compositions and waste compositions of enrichment plants.        
The closest method and soil decontamination facility in terms of technical principle and result (the prototype), reached while applying the method (Atomic Energy, 2007, V. 103, Pub. 6, p. 381-387), includes the following procedures:                soil sampling from contaminated territories;        separation of fraction more than 100 mm;        disintegration (destruction) of soil aggregates and preparation of pulp;        separation of fraction from 3 to 100 mm and fraction less than 3 mm;        hydroclassification (water-gravity separation) of pulp into sand and fine particle fractions with the size of particles more than 0.1 mm and less than 0.1 mm respectively;        flocculation using chemical agents, thickening, dehydration of fine particle fraction;        treatment of circulating water.        disposal of dehydrated fine particle fraction containing radionuclides.        
Sand and coarse (more than 3 mm) fractions can be returned to the soil sampling point.
The facility is composed of modules:                disintegration module provides separation of fraction more than 100 mm, destruction of soil aggregates, preparation of pulp, separation of fraction from 3 to 100 mm and fraction less than 3 mm;        hydroclassification module provides separation of pulp into sand and fine particle fractions with the size of particles more than 0.1 mm and less than 0.1 mm respectively;        thickening module provides thickening of fine particle fraction by adding corresponding agent;        dehydration module (according to the prototype text—filtration) provides removal of excessive moisture from fine particle fraction by press filter;        circulating water treatment module provides separation of fine organo-mineral suspended solids and radionuclides.        
Disadvantages of the Invention:                application of chemical agents for thickening of fine particle fraction increases the volume of rinse waters and consequently costs of process;        mercury gets into the sand fraction in the form of fine drops during decontamination of mercury-containing soils.        